The present invention relates to a signal processing circuit, a physical quantity detection apparatus, an angular velocity detection apparatus, an integrated circuit device, and an electronic instrument.
A gyro sensor is provided in various electronic instruments such as a digital camera, a navigation system, and a mobile phone. An image stabilization process, a dead reckoning process, a motion sensing process, or the like is performed based on the magnitude of the angular velocity detected by the gyro sensor.
In recent years, a reduction in size and an increase in detection accuracy has been desired for a gyro sensor. For example, a vibrating gyro sensor that utilizes the resonance phenomenon of a crystal vibrator has been widely used as a gyro sensor that meets such a demand. Since the detection signal output from the vibrator becomes small along with a reduction in size of such a vibrating gyro sensor, it is very important to reduce noise generated by a signal processing circuit that performs a drive process and a detection process in order to implement high detection accuracy.
The detection process performed by the signal processing circuit includes amplifying and synchronously detecting a small detection signal output from the vibrator, and removing a harmonic component and high-frequency noise using a low-pass filter. A switched capacitor filter (SCF) for which the frequency characteristics are determined by the capacitance ratio and the sampling frequency (clock frequency) is used as the low-pass filter. The switched capacitor filter has an advantage in that a variation in characteristics is small as compared with an RC filter (see JP-A-2008-14932 and JP-A-2008-64663). The sampling frequency fsp of the SCF is set to be equal to the drive frequency fd of the vibrator in order to meet a demand for a reduction in size.
Since noise in a given frequency band (e.g., fd, 2fd, and 3fd) folds back to the DC band due to the sampling process performed by the SCF, noise in such a band is superimposed on the detection signal. Noise that occurs in the SCF is relatively small and can be disregarded. However, noise that occurs in the SCF cannot be disregarded when it is desired to implement a further reduction in noise. The amount of noise the folds back to the DC band can be reduced by increasing the sampling frequency of the SCF. However, since the signal processing circuit normally does not utilize a signal having a frequency higher than the drive frequency of the vibrator, it is necessary to additionally provide a circuit that generates a signal having a frequency higher than the drive frequency. A signal having a frequency obtained by multiplying the drive frequency can be generated by adding a multiplying circuit (e.g., phase locked loop (PLL). However, addition of the multiplying circuit significantly increases the circuit area, so that a reduction in size may not be achieved.